The batch mode vertical hot-wall depressurization CVD apparatus is widely used in IC manufacturing methods in processes for depositing CVD films such as doped-polysilicon film or nondoped-polysilicon film, silicon nitride or silicon oxide films on wafers. The batch mode vertical hot-wall depressurization CVD apparatus (hereafter CVD apparatus) is made up of a vertically installed process tube comprised of an inner tube for containing the wafer and an outer tube enclosing the inner tube, a gas supply tube to feed a film-forming gas in the processing chamber formed by the process tube, an exhaust tube for evacuating gas for a vacuum from the processing chamber, a heater unit installed outside of the process tube for heating the processing chamber, a boat for loading and unloading of multiple wafers into and out of the processing chamber while holding on a multiple step support groove, and a standby chamber for maintaining the boats in standby status for loading and unloading to the processing chamber. After multiple wafers are loaded (wafer charging) into the boat in the standby chamber, the boat is loaded (boat loading) from the standby chamber into the preheated processing chamber, and along with film-forming gas being supplied from the gas supply tube to the processing chamber, the processing chamber is heated to the specified temperature by the heater unit so that a CVD film is deposited on the wafer (see for example Patent document 1).
Boat loading methods for these type of CVD apparatus of the prior art include a boat loading method wherein the processing chamber and the standby chamber are both at atmospheric pressure; a boat loading method wherein the air in the processing chamber and the standby chamber are both purged by nitrogen (N2) gas; and a boat loading method wherein the processing chamber and the standby chamber are evacuated to a vacuum. The boat loading method wherein the processing chamber and the standby chamber are both at atmospheric pressure, tends to easily develop a natural oxidized film during boat loading and therefore has the problem that the oxidized film has adverse effects on the productivity of the IC manufacturing method. The boat loading method wherein the air in the processing chamber and the standby chamber are both purged by nitrogen gas successfully suppresses development of the natural oxidized film compared to the method for boat loading at atmospheric pressure, however oxygen (O2) cannot be completely eliminated from the nitrogen gas so that the natural oxidized film increases to a certain extent. The boat loading method wherein the processing chamber and the standby chamber are evacuated to a vacuum can eliminate virtually all of the oxygen so that an increase in the natural oxidized film is suppressed compared to the method for boat loading under a nitrogen gas environment.
However it was discovered that particles are generated in boat loading that evacuates the processing chamber and the standby chamber to a vacuum. In other words, during boat loading of wafers into the preheated processing chamber, the wafer temperature rises from the periphery on the side near the heater, and rises slower in the center section on the far side from the heater creating a temperature differential. Due to the relation between this temperature differential within the wafer and the wafer's own weight, the wafer is known to curve into a concave shape. Along with this curvature of the wafer, the support surface of the wafer support groove on the boat and the supported surface on the periphery on the lower surface of the wafer rub against each other. When the processing chamber and the standby chamber are evacuated to a vacuum at this time, the frictional force between the boat support surface and the wafer supported surface becomes large so that the film deposited on the lower surface of the wafer in the previous process is peeled away. The film that was peeled away becomes particles and spills downwards from the support surface of the support groove. These particles falling directly downward adhere to upper surface of the wafer where the IC is fabricated and therefore badly affect the productivity in the IC manufacturing method.
The present invention therefore has the object of providing a substrate treating apparatus and a method for manufacturing semiconductor devices capable of preventing a drop in production due to particles from the supported surface of the substrate under decompression.